CODEC devices, capable of encoding and decoding a digital data signal, have been widely used in portable electronic products such as mobile phone and tablet computer. Users of an electronic product may choose different types of loudspeakers, e.g. earphone, home-use or car-use audio, to output sound. Conventionally, the loudspeaker driver can be designed to have a function of estimating the impedance of the chosen loudspeaker, so it may predict the most possible type of loudspeaker. Thus, the driver can estimate a proper power level for the loudspeaker accordingly, to produce sound of comfortable loudness.
However, it takes a long time, usually more than tens of milli-seconds, to perform the impedance detection, and pop-like discontinuous noises may be induced during the detection. Consequently, it is in need to develop a new loudspeaker driving technique.